Technology for determining the location or position of devices that emit radio signals has the potential to provide a wide variety of location-specific applications. For example, in cellular telephone communication networks, the ability to locate a cellular telephone is a critical requirement of emergency (e911) responder systems. Such location systems employ location techniques, many of which are suitable for cellular telephone applications where location precision is not a requirement.
Radio location techniques for indoor radio applications, such as wireless local area networks (WLANs), require generally higher location precision. Some of these location technologies use time-of-arrival (TOA) or time-difference-of-arrival (TDOA) with respect to signals emitted by the device to be located. Other location technologies rely on receive signal strength or path loss between the device to be located and reference devices at known positions that receive the signal emitted by the device.
There is room for improving the accuracy and reliability of location systems that use path loss information to determine the location of a device that emits radio signals detected by other devices at known positions. In particular, some receive signal strength location techniques heretofore known require laborious user assisted calibration of the system by physically walking a transmitter throughout the entire area of interest. Other techniques require numerous transmitter devices placed at known positions in order to assist in calibrating the system. This increases the cost of the system. Furthermore, some systems require imported coverage maps that require a user to manually import information about a space of interest using a software tool that requires the user to trace over a floor plan with a mouse, and to add to that data information describing walls, obstructions, etc.